1. Field of the Invention
The present invention relates to a deflection power supplying apparatus for use in a display and a control method thereof, and more particularly to a deflection power supplying apparatus for use in a display capable of lowering a switching loss and a control method thereof. The present application is based on Korean Application No. 2001-9512, filed Feb. 24, 2001.
2. Description of the Related Art
FIG. 1 shows a circuit diagram showing a conventional deflection power supplying apparatus.
Referring to FIG. 1, the deflection power supplying apparatus includes a rectifying portion 11, a pulse width modulation controlling portion (PWM controlling portion; 13), a first transformer 15, a LC filtering portion 17, a second transformer 19, and a horizontal driver 23.
A first switch 12 is installed to control a power supply to a first coil of the first transformer 15 with the PWM controlling portion 13. Connected in parallel with the first switch 12, a capacitor 14 is aimed to generate resonance in association with the first coil of the first transformer 15. More specifically, the capacitor restricts an increase of voltage at both ends of the first switch 12 at the time of turning off of the first switch 12, and lowers switching loss at the time the first switch 12 is turned on.
A first coil of the second transformer 19 is connected to a second coil of the first transformer 15 to form an electric current loop, while the second coil is connected to a rectifying element to output a high voltage generated by a winding ratio.
Installed on the electric current loop connected between the first coil of the second transformer 19 and the second coil of the first transformer 15, the second switch 25 is switched on/off by a horizontal driver 23.
A deflecting coil 21, called a deflection yoke, is connected in parallel with the second switch 25 to form electric loop.
The element designated by a reference symbol S.R is an inductor for suppressing a parasitic component.
The deflection power supplying apparatus described above is generally called a pseudo-resonant flyback converter. In the deflection power supplying apparatus, electric current is applied to the first transformer 15 in a discontinuous current mode, and the maximum electric current at the first switch 12 is increased to more than twice the value of a normal load electric current. Further, since the maximum value of the switching voltage at the first switch 12 is the result of adding output voltage of input voltage at the first coil, switching stress is increased, deteriorating power transfer efficiency.
Additionally, due to the considerable number of components, the structure becomes complicated. Also, since the switches are driven by the variable-frequency method, it is difficult to design the LC filter 17 in order to improve filtering capability.
FIG. 2 is a circuit diagram showing a conventional deflection power supplying apparatus according to another method.
Referring to FIG. 2, the deflection power supplying apparatus includes a rectifying portion 31, a pulse width modulation controlling portion (PWM controlling portion; 33), a LC filter 37, a high voltage transformer 39, and a horizontal driver 43.
A first switch 32 is installed to control a power supply from the rectifying portion 31 to a first coil of the high voltage transformer 39 with the PWM controlling portion 33.
The LC filter 37 is connected between the first switch 32 and the first coil of the high voltage transformer 39, to suppress noise input through the first switch 32 and noise directed from the high voltage transformer 39 to the rectifying portion 31.
The second coil of the high voltage transformer 39 is connected to the rectifying element, to thereby output high voltage generated by the winding ratio.
The second switch 45 is installed on the electric current path connected from the first coil of the high voltage transformer 39 to the rectifying portion 31, and switched on/off by the horizontal driver 43.
The deflecting coil 41 is connected in parallel with the second switch 45 to form an electric current loop.
The deflection power supplying apparatus as described above is generally called a buck converter. The operation of the buck converter will be described below.
The PWM controlling portion 33 controls duty, a ratio of the interval, where the first switch 32 is driven on, with respect to the driving period, according to required electricity supply, and drives on/off the first switch 32.
The maximum electric current input through the first switch 32 is determined as a normal load electric current driven in a continuous current mode, and the maximum voltage at both ends of the first switch 32 are determined as input voltage.
The high voltage transformer 39 induces energy stored at the first coil through the LC filter 37 for smoothing and noise removal to the second coil by the flyback method, generating high voltage. The energy, induced at the second coil of the high voltage transformer 39, is output as high voltage for thermal electron emission.
The horizontal driver 43 regularly drives on/off the second switch 45 in accordance with the frequency of the horizontal sync signal. While the second switch 45 is turned on, energy is stored at the first coil of the high voltage transformer 39, and the deflecting coil 41 generates the electric current required for horizontal scanning of a screen. While the second switch 45 is turned off, the energy stored at the first coil of the high voltage transformer 39 is transmitted to the second coil, and the deflecting coil 41 generates retrace electric current that is required to emit a beam to a horizontal scanning upper end.
Since the deflection power supplying apparatus as described above, however, can not share the functions of some elements, the structure becomes complicated. Further, when the energy stored at the first coil of the high voltage transformer 39 flows toward the LC filter 37, i.e., when the energy flows in the reverse direction during the time the first and the second switches 32 and 45 are switched off altogether, energy is almost charged through the capacitor 37a. As a result, switching loss occurs when the first switch 32 is turned on, and it is hard to control the generation of the switching noise.
The present invention has been made to overcome the above-mentioned problems of the related art, and accordingly, it is an object of the present invention to provide a deflection power supplying apparatus for use in a display and a control method thereof capable of simplifying a structure for supplying deflection electric current and also lowering switching loss.
The above object is accomplished by an apparatus for supplying a deflection power for use in a display in accordance with the present invention, including a rectifying portion for rectifying an alternating electric current into a direct electric current, a high voltage outputting portion having a first coil connected on an output path of a voltage rectified by the rectifying portion and a second coil coupled with the first coil, the high voltage outputting portion for outputting a voltage induced at the second coil, a first switching portion installed between the rectifying portion and the first coil, for controlling a power supply, a second switching portion installed on a path formed from the first switching portion, the first coil, and the rectifying portion, for controlling the power supply, and a deflection electric current generating portion forming a loop of electric current in parallel in association with both ends of the second switching portion, the deflection electric current generating portion connected in series with a deflection coil and a capacitor.
The high voltage outputting portion includes a diode, an anode of which being connected to one end of the second coil, and a capacitor connected between a cathode of the diode and the other end of the second coil.
Further, the deflection power supplying apparatus includes a diode and a capacitor connected in parallel with the both ends of the second switching portion.
Preferably, the deflection power supplying apparatus includes a free wheeling diode having one end connected between the first switching portion and the first coil and the other end connected to the end of the rectifying portion which is not connected to the first switching portion.
A main controlling portion controls the first switching portion and the second switching portion such that the first switching portion is turned on almost simultaneously with the second switching portion, and the second switching portion is driven on/off in accordance with a horizontal deflection frequency of the display.
The main controlling portion controls the switching portions to sequentially repeat a cycle of a first mode, a second mode, and a third mode, the first mode in which the first switching portion and the second switching portion are turned on in accordance with a horizontal sync signal almost simultaneously, the second mode in which the first switching portion is turned off while the second switching portion remains in an off state, and the third mode in which the first switching portion and the second switching portion are turned off.
The above object is also accomplished by a method of driving an apparatus for supplying deflection power in accordance with the present invention, including the steps of almost simultaneously turning on the first switching portion and the second switching portion in accordance with a horizontal sync signal, turning off the first switching portion, while keeping the second switching portion in an on state, turning off the first switching portion and the second switching portion, and repeating the above three steps at least once.